1. Field of Invention
The present invention relates to underwater actuators and their control.
2. Background of the Invention
Underwater actuators may be required to be operated quickly. Actuators that use control fluids require a pressure source that is higher than the ambient pressure at the operating depth in order to operate. The pressure sources include pumps and gas charged accumulators. High flow pumps are required to operate high flow demand fluid actuators. However, accumulators may lose efficiency due to adiabatic discharge under high flow demands. As water depth increases, these devices become less efficient.
Existing designs have focused on increasing the efficiency of the positive pressure portion of the system that acts on the actuator piston and have ignored the potential to use the pressure generated at a depth as a source to operate the actuator. This focus has resulted in using either/or a combination of larger pumps, accumulators with higher gas pre-charge pressures, changing the pre-charge gas to helium instead of nitrogen, adding accumulators or increasing accumulator working volume capacity by using depth compensated accumulators in deep water. In deep water operations, these solutions decrease efficiency and reliability, add weight (by adding larger pumps or more accumulators), increase logistics issues (using helium instead of nitrogen as the pre-charged gas), or add complexity and potential for seal leakage due to cycling (depth compensated accumulators).
The inventor previously filed and was granted U.S. Pat. No. 8,726,644 where he employed a device, called a sub-actuator, which utilized a gas volume near atmospheric surface pressure, or lower to supply substantially a vacuum when the device is positioned for use at depth. This gas, at the lower pressure, coupled with fluid at depth or ambient pressure, and fluid at a high pressure, supplied by accumulators, umbilical lines, or other other methods, allowed the sub-actuator to assist in operation of an actuator in various situations with more precise control than has previously been accomplished in the industry. However, the sub-actuator and coupled actuator do not provided a simplistic compact package as desired in the industry.